1. Field of the Invention
The present invention relates to a micro positioning device, and more particularly to a micro positioning device of a writing head drive system in a servo rack writer for writing on a track for a hard disk drive unit.
2. Related Background Art
A conventional hard disk drive unit writes on a servo track by using a DC motor for driving a read/ write head for a hard disk drive unit itself, because the storage capacity is not relatively very large. However, since the servo track pitch serves as a reference for recording or reproducing the information, it must be made less than a read/write pitch for the hard disk drive unit. However, at the resulting higher density, there is a tendency that it is difficult to operate the head disk drive unit when it is internally provided from the viewpoint of positioning accuracy. As a result, a special-purpose servo track writer for writing the track during the manufacture thereof is necessary.
When a special-purpose servo track writer is used, a method is generally adopted in which the head which is internally provided, is driven by means of an external drive unit, with an actuator for operating the head pressed against a support member of the head. Such a conventional example is shown in FIG. 4. In the same figure, 1 is an encoder motor, of which 1A is an encoder portion and 1B is a motor portion. 2 is a drive disk to be driven by the encoder motor 1, and 3 is a drive pin. 4 is a hard disk drive unit. In a factory, such drive units 4 are conveyed in sequence on a belt conveyor (not shown) to the servo track writer 1-3. 5 is a hard disk within the drive unit 4, 6 is a head arm, and 7 is a linear motor. The track data is written onto the hard disk 5 by means of a head 8 installed at a leading end of the head arm 6, with the drive pin 3 abutting against the head arm 6, while moving the head arm 6 circularly around a fulcrum 10 with the encoder motor 1. The track data is transmitted from a data transmission device 11 located outside of the above members to the head 8. Here, the servo track writer is constituted of the above members 1 to 11, and the hard disk 5 and the linear motor become a hard disk as the product.
In this way, in recent years, the servo track writer with the constitution as shown in FIG. 4 has been used along with the higher density servo track, whereas the hard disk drive unit 4 of FIG. 4 is conveyed on a manufacturing line but not fixed at any time. Accordingly, in such a device that temporarily connects, so to speak, the moving member and the stationary member such as the servo track writer 1-3 as shown and performs the positioning operation with a high precision, there was a significant problem to be solved that the high precision in writing the servo track was difficult to maintain stably, due to the instability of the connection, if the connecting portion was badly secured.
Conventionally, in a device using a plurality of D/A converters, when the D/A converters of n-bit parallel data input were used, n data signal lines for each D/A converter were used. Also, when D/A converters of serial data input were used, the serial data signal line was prepared one for each D/A converter, the read timing of which was determined with its control signal.
Conventionally, in a device using a plurality of D/A converters, data was separately input into respective D/A converters. Accordingly, for D/A converters of parallel input, (number of bits) x (number of D/A converters) of data input lines are necessary. Also, for D/A converters of serial input, data input lines as many as the number of D/A converters are necessary, resulting in the occupying a large area on a substrate. Also, in practical use, there are many cases where a board on which the D/A converters are mounted and a board on which data are created for input into the D/A converters are separated from each other, requiring a number of long signal conductors, and thereby running the risk of disconnection of the conductors or noise.
Also, conventionally, a precision micro positioning device is often used in a laser interferometer, and in which are arranged a plurality of expensive optical devices, scanning the laser beam with a gas laser.
The laser interferometer method as above mentioned was required to have a large space for the arrangement, because there are disposed a gas laser oscillator, an interferometer, optical devices such as a corner cube, and instruments, over which the laser beam scans. Furthermore, because of the interferometer used, there are some changes in the characteristics due to the temperature variation or fluctuation of air flow, so that it is necessary to be used in a clean room. Owing to the above-described large restriction, that is, the restriction on the space and service environment, the laser interferometer method is consequently very costly.
Also, conventional positioning devices generally use a PWM type driver for driving the motor in order to increase the power efficiency. In a circuit for controlling the motor, an analog loop control circuit is used for real time processing.
However, in the above example, there are the following drawbacks in positioning with high precision.
As the motor driver is used with the PWM method,
(1) high frequency noise is produced as a result of the switching operation, destroying the linearity in a minute area, so that it is difficult to obtain an excellent controllability. PA1 (2) there is a limitation in positioning with high precision because the characteristics (precision, noise, temperature) of the elements used may have direct effects on the system characteristics. PA1 (3) the change of elements for use over time has an immediate effect on the system characteristics, shortening the life of the system. PA1 (4) the analog loop control circuit does not allow the implementation of a complex algorithm necessary in positioning with high precision.
Also, as the control circuit is an analog loop control circuit,
The fine adjustment of the characteristics requires great skill, and takes several processes, and